PS: your WP version seems a bit old, but I do not know anything about WP, just checked their site and as of 21 june 2013, the latest advertised is 3.5.1 and there is quite a big fat warning about the rest not being safe to use.

I updated guide added brotli + curl silent. But I really can’t see any situation where HEAD request with Accept-Encoding does not work? HEAD response shouldn’t be compressed and your web server doesn’t work right if it doesn’t tell to client (browser) what encoding it uses.

If you send plain HEAD request without Accept-Encoding, then server usually omit content-encoding, like stackoverflow discussion says, but actually original question is about the request headers and this guide CURL command send request header -H 'Accept-Encoding: br,gzip,deflate' and check response headers Content-Encoding: so this is totally different thing.

If you think situation where browser sends request with ‘Accept-Encoding: br,gzip,deflate’ and your web server response is gzipped, but there is no Content-Encoding: header your browser shows gzipped response as plain text. So if you really can’t see content-encoding header on HEAD response when you use accept-encoding request header, then you really should check your web server configuration and fix it!!